1. Field of the Invention
The present invention relates generally to the fields of immunology and pathology. More particularly, it concerns methods and compositions involving the LcrV protein from Yersinia bacteria, particularly LcrV proteins that can be used to invoke an immune response against the bacteria while reducing the immunosuppressing effect of the native protein in a subject, as well as those that can be used because of their immunosuppressing effect. Therefore, the present invention includes preventative and therapeutic methods and compositions involving LcrV proteins.
2. Description of Related Art
Yersinia pestis is the causative agent of plague, a disease which likely killed more people worldwide than any other disease.
Early attempts at plague immunization employed avirulent live plague bacilli such as the non-pigmented EV76 strain (Meyer, 1970; Welkos et al., 2002). This approach was effective to prevent bubonic plague but too frequently resulted in complications such as inflammation, if not modest infection or even death (Bartelloni et al., 1973; Russell et al., 1995). Nevertheless, the process was utilized until recently in the Soviet Union even though numerous booster immunizations are required for full effectiveness. A similar, but less successful approach was the use of killed organisms in the United States (Williams and Cavanaugh, 1979). The general failure of these approaches has promoted considerable effort towards development of soluble subunit vaccines containing one or more protective antigens (Russell et al., 1995; Titball and Williamson, 2004). Vaccination with purified recombinant LcrV, a known protective antigen, elicits an immune response that protects experimental animals against plague (Une and Brubaker, 1984; Motin et al., 1994; Motin et al., 1996; Heath et al., 1998; Anderson et al., 1996; Leary et al., 1995). Other preparations of LcrV, whether alone or as a fusion to the Caf1 (F1) pilin subunit (Heath et al., 1998), extended these observations, revealing that antibodies against LcrV provide protection against bubonic and pneumonic plague.
Nakajima and Brubaker demonstrated that Y. pestis infection in mice is associated with the suppression of endogenous TNF-α and IFN-γ in vivo (Nakajima et al., 1995; Nakajima et al., 1993). Further, exogenous supply of TNF-α and IFN-γ, of rabbit polyclonal antisera against LcrV or of monoclonal antibody against LcrV could protect animals from a lethal infection with Y. pestis (Nakajima et al., 1995). Injection of purified recombinant LcrV preparations unequivocally demonstrated that LcrV functions as a protective antigen for plague and that antibodies against LcrV can be passively transferred to naive animals to achieve the same effect, which involves simultaneously the blockade of IL-10 secretion and restoration of endogenous TNF-α and IFN-γ release during animal infections with plague bacilli in vivo (Nakajima et al., 1995).
LcrV is absolutely required for human or animal infectious disease of three pathogenic Yersinia species, Y. enterocolitica, Y. pseudotuberculosis, and Y. pestis (Skrzypek and Straley, 1995; Bergmann et al., 1991; Lee et al., 2000). Heesemann and colleagues showed that Toll-like receptor 2 (TLR2) and CD14, but not TLR1 or TLR4, were required for Yersinia release of IL-10, and that deletion of the TLR2 gene resulted in resistance of mice to infections with pathogenic Yersinia spp. (Sing et al., 2002a; Sing et al., 2002b; Sing et al., 2003). Taken together, these observations not only document the central importance of LcrV in disease establishment, in modulating host immune functions and its use as a protective vaccine antigen, but also point to suppression of host immune responses as a serious obstacle for the vaccination of humans with purified recombinant LcrV.
To identify minimal components for plague vaccines, presumed linear epitopes of LcrV were divided into peptide segments of 30 amino acids or into truncated LcrV molecules lacking 100 or more amino acids (Pullen et al., 1998; Hill et al., 1997). Together these studies showed that immunization with small linear peptide epitopes (30 amino acids) provides no protection against plague, whereas large truncations of LcrV can elicit at least some protective immunity. However, previous studies did not take into consideration LcrV-mediated EL-10 release, and left unresolved whether plague vaccines without immune suppressive properties can be generated (Pullen et al., 1998; Hill et al., 1997). Therefore, there is a need for immunogenic compositions and methods that will elicit an immune response against pathogens such as Yersinia pestis but have less severe or negative immunosuppressing side effects.